Disposable absorbent products currently find widespread use in many applications. For example, in the infant and childcare areas, diapers and training pants have generally replaced reusable cloth absorbent articles. Other typical disposable absorbent products include feminine care products such as sanitary napkins, panty shields, or tampons; adult incontinence products; and health care products such as surgical drapes or wound dressings. A typical disposable absorbent product generally comprises a composite structure including a top sheet, a back sheet, and an absorbent core structure between the top sheet and back sheet. These products usually include some type of fastening system for fitting the product onto the wearer.
The use of water-swellable, generally water-insoluble absorbent materials, commonly known as superabsorbent polymers (“SAP”), in disposable absorbent personal care products is known. Such absorbent materials are generally employed in absorbent products in order to increase the absorbent capacity of such products while reducing their overall bulk. Such absorbent materials are generally present in absorbent products in the form of small particles in a fibrous matrix, such as a matrix of wood pulp fluff. A matrix of wood pulp fluff generally has an absorbent capacity of about 6 grams of liquid per gram of fluff. The superabsorbent materials generally have an absorbent capacity of at least about 10, preferably of about 20, and often of up to 100 times their weight in water. Clearly, incorporation of such superabsorbent materials in disposable absorbent products can reduce the overall bulk while increasing the absorbent capacity of such products.
The absorbent products mentioned above, such as baby diapers, adult incontinence devices, and feminine hygiene products, may be made with a cellulose fiber fluff-based absorbent core sandwiched between a liquid pervious top sheet, which allows the unobstructed passage of fluid to the absorbent core, and a liquid impervious backing sheet usually of plastic material, which contains the absorbed fluid and prevents it from passing through the absorbent core and soiling the undergarments or clothing of the wearer of the absorbent article.
The absorbent core of these absorbent articles may be constructed of defiberized wood pulp with or without superabsorbent polymer granules. The absorbent core may be formed on a pad-forming unit of a converting machine on a carrier tissue to facilitate processing. Some absorbent core forming units are equipped with layering capability in which a second discrete fluff layer may be laid over a primary fluff-based absorbent layer to form a multi-layer absorbent structure. In these absorbent structures, the primary layer may include loose, superabsorbent polymer granules. It is believed that commercially used superabsorbent polymer granules typically have a coarse size distribution. For example, Atofina reported on its website (www.aquakeep-sap.com) on Oct. 15, 2001, that its AQUAKEEP® superabsorbent polymers may be used in diapers and adult incontinence products and have a particle size distribution of less than 0.5%<45 microns, less than 3%>850 microns; with an average particle size distribution of around 420 microns. Such particle size distribution contains a large amount of particles below 850 microns.
In recent years, market demand for thinner and more comfortable absorbent articles has increased. Ultra-thin feminine napkins are no longer constructed from loose wood pulp, which tends to give a bulky product, but with a roll good-based air-laid absorbent cores in which a roll or coil of preformed absorbent core material is unwound directly onto the absorbent pad-making machine without the defiberization step required for fluff-based products. The roll good-based approach results in a product thinness, which cannot be achieved by loose fluff-based technology. As will be seen later, the present invention can produce thinner absorbent products that have the same absorbance properties as thicker products.
Another alternative to using a fibrous matrix containing superabsorbent materials, absorbent foam composites are also known. One form of an absorbent foam composite is wherein a foam material, such as polyurethane, is prepared to include a particulate superabsorbent material within the structure of the polyurethane foam. Alternatively, a particulate superabsorbent material is located between at least two layers of a polyurethane foam material to form a layered composite structure.
U.S. Pat. No. 5,985,434, entitled “Absorbent Foam”, is described to be an improvement to the foamed materials mentioned in the preceding paragraph.
U.S. Pat. No. 6,241,713 entitled “Absorbent Structures Coated with Foamed Superabsorbent Polymer” is described to involve coating a layer of a foamed hydrogel-forming polymer having superabsorbent properties on the surface of a sheeted fibrous absorbent material suitable for use in disposable absorbent products.
U.S. Pat. No. 5,720,832, entitled “Method of Making a Meltblown Nonwoven Web Containing Absorbent Particles”, describes yet another approach to the field of the present invention. This patent may contact freshly extruded microfibers with particles that may be composed of superabsorbent materials. The particles are electrostatically charged and applied to the fibers while such fibers are still tacky following extrusion. The result of such application appears to be a physical adherence of the powder to the wet fiber. Adherence can include embedding the particles into the fiber surface when an embossing technique is used.
U.S. Pat. No. 5,419,955 involves the use of superabsorbent particles and sheets to improve absorbency and retention properties. This technique forms a suspension of the particles to avoid problems with powder agglomeration and powder loss.
The invention of this application avoids the need for tacky, freshly extruded fibers as a starting material in a simple, straightforward manner. Typically such freshly extruded fibers are believed to be sufficiently tacky to function as described in aforementioned U.S. Pat. No. 5,720,832 for less than about one minute following extrusion. Thus, a very narrow processing window exists. Fibers or other materials that have been made and stored over a period of time longer than about one minute prior to coating and powder coating may be utilized in this invention. Also, while the need to use particle-containing suspensions is avoided, the objectives of avoiding powder agglomeration and powder loss are achieved by this invention. Accordingly, the objectives of the prior art are achieved without the accompanying constraints.
Superabsorbent polymeric particles, tablets, and emulsions have been used for the purposes of minimizing the loss of water and nutrients in soils, for erosion control, and in combination with irrigation procedures. However, none of these uses appear to involve adhering superabsorbent powders on a substrate or a substrate having openings extending through the substrate. Solid or fibrous polymeric films, such as sheets or strips, or of any other desired shape or form, constitute a suitable substrate. The above-described uses appear to merely involve the dispersal of superabsorbent polymeric particles in soil and other growing media. Erosion control is believed to employ dispersed particles and/or perforated sheet-like barriers. Neither of these techniques appears to involve the combination of the invention, i.e., adhered superabsorbent polymeric powder stably coated on a substrate.